When driving a large-capacity motor, it is necessary to increase the capacity of a PWM power converter (hereinafter referred to as an inverter) that controls speed and torque of the motor. One way to increase the capacity of the inverter is to connect the outputs of a plurality of inverters in parallel to increase an output current.
In the case of a single winding motor, each inverter drives the motor via a coupling reactor. Then output current is unbalanced due to individual switching difference of the inverter element, variation in cable impedance. This unbalance causes unnecessary circulating current called cross current between the inverters.
As a control method for suppressing this cross current, there are Patent documents 1 and Patent document 2. These are to reduce the size of the coupling reactor on the premise that the cross current suppression control gain is appropriately set, and these are not the methods that enables the motor to be driven by parallel connection of inverters in a reactor-less manner.
In addition to the above, as a cross current suppression control method that enables parallel operation with reactor-less operation, there are methods described in Patent document 3. In the case where the object to be driven is a multi-winding motor, by using the magnetic coupling between the stator windings as a substitute for the reactor, it is possible to obtain a reduction in size and cost reduction effect of the reactor due to reactor-less way.